Summary

Background

The best approach to discontinuing mechanical ventilation in intubated patients has not been definitively determined. This randomized study was designed to examine a particular protocol designed to expedite the discontinuation of mechanical ventilation. The patients were screened to determine when they might be ready for extubation. Then, if indicated by screening, the patient underwent a trial of unassisted ventilation. If a patient successfully completed that trial, the responsible physician was notified.

Methods

Subjects: Patients over 18 years of age in the medical or cardiac intensive care units of an 806-bed university hospital, who had been on a respirator for less than 2 weeks at the time or randomization. 300 patients were enrolled between June, 1995 and February, 1996; 149 to the intervention group, 151 to the control group.

Interventions: All 300 patients underwent daily morning screening of respiratory function by a respiratory therapist. The results of this screening were not made available to the attending physician(s) responsible for the patient's care.

Control group: the screening was the only intervention performed on the patients.

Intervention group: patients who "passed" the screening test, went on to a trial of unassisted breathing.

In order to pass the screening test, five criteria had to be met:

ratio of pO2 to FiO2 > than 200

PEEP < 6 cm water

cough during suctioning present

ratio of respiratory frequency to tidal volume not greater than 105 breaths per minute per liter

patient not on vasopressor or sedative infusions

The trial of spontaneous breathing required the intubated patient to breathe without mechanical assistance, but with the same level of PEEP and the same inspiratory oxygen concentration as previously. The breathing trial was discontinued if the respiratory rate exceeded 35 per minute, oxygen saturation dropped below 90%, heart rate was above 140 or changed by over 20%, blood pressure was over 180 mmHg or under 90 mmHg, or if there was increased anxiety or diaphoresis.

If the patient tolerated this trial for two hours, it was deemed successful. The attending physician was notified orally and a note was placed in the chart stating that the patient had an 85% chance of staying off mechanical ventilation for 48 hours. If the patient did not tolerate the trial, the whole process was repeated on subsequent days.

Analysis: Primary outcomes, defined a priori, were overall length of mechanical ventilation, time from successful screening to discontinuation of ventilation and ICU length of stay.

Secondary outcomes were the frequency of complications (re-intubation, ventilation for more than 21 days, tracheostomy, extubation by the patient), costs, length of hospitalization and deaths.

Results

At baseline, patients were relatively well matched in the two groups. The average age was 61 years. Overall, 21% were treated in the CCU, 79% in the ICU. Patients in the intervention group were slightly sicker than those in the control group (APACHE II score 19.8 vs. 17.9; acute-lung-injury score 1.9 vs. 1.7). Causes of respiratory failure and modes of ventilation did not differ significantly.

Consistent with the greater severity of illness in the intervention group, the median time from intubation to a successful screening test was 3 days in the intervention group and 2 days in the control group. The median number of days from the successful screening test to extubation was 1 day in the intervention group and 3 days in the control group (p<0.001). 48 hours after a successful screening test, 65 patients in the intervention group were extubated, vs. 24 patients in the control group. Overall, the median duration of mechanical ventilation was 4.5 days in the intervention group, vs. 6 in the control group.

There were fewer complications overall in the intervention group (20% vs. 41%), including fewer re-intubations and fewer patients requiring prolonged intubation. Mortality was similar in both groups (38% in the intervention group, 40% among controls).

Costs, days in intensive care and length of hospitalization did not differ significantly between the two groups, although all were non-significantly lower in the intervention group.

Authors' Discussion

The authors conclude that respiratory screening followed by a trial of unassisted ventilation produced better results than traditional "weaning" from the respirator. They note that one previous trial of unassisted ventilation produced similar results, whereas another one found pressure-support ventilation to be superior to unassisted ventilation and intermittent mandatory ventilation. Despite the earlier extubation in the intervention group, re-intubation was less frequent in this group. Finally, they stress the important role of non-physician health professionals in the care of these patients.

Editorial

In an accompanying editorial, John M. Luce from San Francisco General Hospital points out that mechanical ventilation is an effective technique, but comes at a price. In order to reduce the reliance on mechanical ventilation, we need to fully exploit non-invasive face-mask techniques, apply intubation only when appropriate and discontinue it as soon as feasible. This study supports the use of a protocol in helping discontinue mechanical ventilation and Dr. Luce argues that such protocols, particularly in intensive care settings, can decrease the cost and increase the quality of care.

Comment

One methodologic problem with this study is related to physicians' awareness of the ongoing trial and their reaction to it. Since 300 patients were enrolled over a 9 month period in two intensive care units, one must assume that most of the physicians taking care of ICU patients took care of a significant number of study patients. Were they aware of this ongoing trial? This is not specifically addressed in the article.

If the attending physicians were aware of the trial and of its purpose, they would have been unblinded as to group assignment, at least for the intervention group. Such unblinding can lead to treatment bias, since the attitude towards respiratory management could be influenced by this knowledge. If the attendings were not aware of the trial, they must have noticed that some of their patients were successfully passing trials of unassisted ventilation and some were not; they could have misinterpreted the fact that patients (controls) were not passing these trials as indicating a poor prognosis for weaning, and consequently delayed any attempts at extubation. Thus, the degree of blinding of the attending physicians is an important issue, which was not discussed in the article.

A second methodologic issue relates to the fact that in the intervention group the attending physicians were given a message from a third party concerning patient management, whereas in the control group no such message was conveyed. Such third-party messages presumably exert pressure on the recipient to change his/her behavior. Thus, the shorter time to extubation in the intervention group was probably the result of a combination of two factors: the protocol that was applied and the pressure to extubate communicated by the message. From this trial design, there is no way to quantitate the relative contribution of these two factors.

In the editorial, Dr. Luce states that the trial "demonstrates that the systematic application of a protocol for discontinuation of mechanical ventilation yields better outcomes ... than are achieved by relying on the judgement of a physician alone". It should be borne in mind, however, that another study of strategies for weaning patients from respirators found a different approach to be more effective. Also, as mentioned above, some of the benefit from this trial is probably due to the impetus provided by a third-party notification and some of it may be due to the effect of the trial itself on physician behavior.

I agree with your comments on methodology but one must concede it is hard to
objectively study weaning and treat patients at the same time.
I still think the major problem with this study is that it represents a
study of what is a bad practice. The drive to get people breathing
spontaneously and off
a ventilator should be a major role of intensivists and once a day
assessment is totally inadequate. A further major compounding factor is that
the goal of extubation may be delayed until a "safer" time than 0200
depending on available staff, or delayed because a patient is going
somewhere and leaving the tube in a little longer may make this safer. In
our post bypass unit the nurses follow a protocol where assessments are made
hourly and ventilation changes and extubation follow a logical pattern and
most are extubated in the first 24 hours postoperative (and most of them in
the first 12 hours). No doctor is necessary.

A similar practice may not be in the best interests of a quad, asthmatic, or
patient with Guillain Barre. Some patients are ventilated for transport or
to have CT/MRI and can be extubated on arrival on MV criteria alone.
To determine a patient can breathe spontaneously and them contact the "name
on the end of the Bed" to decide what to do next is to me very far from "best
practice" and I believe that decision should be made by the person capable
of making the assessment. If the patient can breathe spontaneously they
should be extubated NOW rather than wait for "Sir" to finish his rooms and
come in for the evening round and pontificate. To do otherwise is cruel, and
foolish.